1. Field of Invention
The present invention relates to a method for an all-dry low temperature process for removal of inorganic, organic and polymer residues on the top surface and sidewalls of a semiconductor wafer after the metal etch.
2. Description of Related Art
In the semiconductor wafer manufacturing art, removal of photoresist is generally accomplished by using a combination of dry and wet processes. For example, a typical photoresist removal procedure comprises the use of an oxygen-plasma ashing followed by a wet chemical clean step using an organic solvent at high temperature.
During the ashing step the organic matrix of the photoresist is removed, thereby leaving metal-ion contaminates particles and un-ashable polymers behind. Consequently, a wet clean is generally needed to remove these leftover residues. The "wet clean" removal of these residues requires organic solvents and other hazardous, reactive chemicals such as concentrated sulfuric acid. Nevertheless, in all to many instances, these residues still persist and remain present on the wafer surface or the etched features.
Accordingly, removal after metal etch has always been a significant challenge. Further, the high temperature ash resulting from oxygen plasma ashing causes oxidation of polymeric residues (especially inorganic residues) thereby making it more difficult to remove.
Del Puppo et al., Photoresist Removal Using Gaseous Sulfur Trioxide Cleaning Technology, 3677 (Pt. 2) Proc. SPIE-Int. Soc. Opt. Eng. At 1034-1045 (1999) disclose a process for photoresist removal using SO.sub.3 is disclosed. This non-plasma method uses anhydrous sulfur trioxide gas in a two-step process, during which, the substrate is first exposed to SO.sub.3 vapor at low temperatures &lt;150.degree. C. and then rinsed with de-ionized (DI) water. The removal of the modified photoresist takes place during the subsequent DI water rinse step.
While the Del Puppo et al. SO.sub.3 process removes photoresist and polymer residues, as is confirmed in the disclosure of U.S. Pat. No. 5,952,157, this method for removing a photoresist film using anhydrous SO.sub.3, more often than not, does not remove inorganic elements (see FIG. 9 and column 1, lines 34-50).
A method for removal of photoresist residue after dry metal etch without requiring excessive high temperatures or extensive re-work cycles is disclosed in U.S. Pat. No. 5,770,523. However, this method for removal of the surface layer of the residual photoresist mask pattern for metal subtractive etching employs fluorine-containing reactive gases to form volatile compounds with the surface layer, and subsequently uses conventional oxygen plasma stripping to complete resist residue removal, and is encumbered by the detriments of using conventional oxygen plasma stripping processes.
A process for polymer removal from top surfaces and side walls of a semiconductor wafer is disclosed in U.S. Pat. No. 5,780,359 in which the photoresist and residue are processed simultaneously by a chemical mechanism comprising reactive species derived from a microwave-excited fluorine-containing gas and a physical mechanism comprising ion bombardment resulting from a radio frequency excited plasma.
U.S. Pat. No. 5,709,755 disclose a method for chemical-mechanical polishing (CMP) of a wafer comprising: passing the wafer from a CMP polishing station to a APM rinse station (APM is a solution of ammonium hydroxide and hydrogen peroxide in water); brushing and rinsing (with APM) both sides of the wafer, to thereby remove a large part of the CMP residue; passing the wafer to a DI (de-ionized water) rinse station, and brushing and rinsing (with DI) both sides of the wafer, thereby removing yet more of the CMP residue.
In the art of residue removal after metal etch, in which the use of anhydrous SO.sub.3 gas followed by rinsing with de-ionized water is not a reliable method for removing resist films containing inorganic elements, and in which dry etching methods are known to give rise to plasma irradiation damage, and in which plasma ashing involves high substrate temperatures (&gt;180.degree. C.) which tends to enhance the problem of drive-in contaminates, and in which chemically modified top layers of the resist in which the crust is too hard to remove using standard oxygen plasma, and in which the use of fluorine addition to the plasma enhances the ashing capability that often results in substrate damage, there is a need to by-pass, avoid, or eliminate these drawbacks after metal etch.